1. Field of the Invention
The present invention relates to a rotation-magnetron-in-magnetron (RMIM) electrode, a method of manufacturing the RMIM electrode, and a sputtering apparatus including the RMIM electrode. More particularly, the present invention relates to an RMIM electrode appropriate for a semiconductor device technique providing a high integration density and a low line width and a large-sized wafer process in a magnetron sputtering method, a method of manufacturing the RMIM electrode, and a sputtering apparatus having the RMIM electrode.
2. Description of the Related Art
Physical vapor deposition (PVD) and chemical vapor deposition (CVD) are generally used to manufacture thin films having a fine thickness. In a CVD method, a thin film having desired characteristics is obtained through chemical reactions. Alternately, in a PVD method, a thin film is formed by applying energy to a desired material so that the desired material gains kinetic energy and can then be deposited on a wafer.
In general, there are two different types of CVD methods, i.e., sputtering and evaporation. In an evaporation method, a solid or liquid is heated so that it can be divided into molecules or atoms, and then the molecules or atoms are condensed on the surface of a wafer. An evaporation apparatus has been widely used to manufacture semiconductor devices because it has a simple structure and can be applied to a variety of materials.
A second CVD method, sputtering, is a method of depositing a thin film on a wafer in which particles having a high energy are made to collide with a target formed of a desired material, thereby causing the desired material to be emitted from the target and deposited on the wafer. Sputtering can be used to form a thin film having a relatively uniform thickness on a large area and is easier than other deposition methods to control a composition ratio of a thin film when forming the thin film of an alloy. Therefore, sputtering has been widely adopted in the manufacture of semiconductor devices, such as dynamic random access memory (DRAM), static random access memory (SRAM), non-volatile memory (NVM), LOGIC, and other electronic devices.
There are various types of sputtering, including a bipolar sputtering method and a magnetron sputtering method, which are the most widely used methods. Use of a radio frequency (RF) or direct current (DC) bipolar sputtering method is simple, however, it takes a relatively long time to form layers, and during the formation of the layers, an increase in temperature, damage to layers, or component separation may occur. In order to solve the disadvantages of the bipolar sputtering method, the magnetron sputtering method has been developed.
The magnetron sputtering method is a method of generating high-density plasma by applying a parallel magnetic field onto the surface of a target and thus trapping electrons in an area near a cathode, i.e., the target. In the magnetron sputtering method, unlike in the bipolar sputtering method, it is possible to deposit layers at high speeds and prevent the temperature of a wafer from increasing by controlling secondary electrons. In addition, in the magnetron sputtering method, a high-density plasma environment with a low pressure can be generated inside a reactor using a magnetic field, and thus step coverage can be improved by promoting a tendency of sputtering particles to travel straight so that the sputtering particles can be effectively deposited on a region having a step difference.
FIG. 1 is a diagram illustrating a conventional magnetron sputtering apparatus. Referring to FIG. 1, a wafer holder 19 on which a wafer 17 is mounted is placed inside a vacuum chamber 21, and a target 11 is placed facing the wafer holder 19. In the magnetron sputtering apparatus, magnets 15 are arranged on a rotation plate 29 behind the target 11, thus generating magnetic field lines in a predetermined direction. In addition, a power supply 27 is provided outside the vacuum chamber 21 so that voltage can be applied to an electrode 13 on the target 11. A balance weight 16 is provided on one end of a rotation plate 29 to compensate for the weight of the magnets 15 so that the rotation plate 29 can rotate in balance.
If the chamber 21 is maintained at a predetermined vacuum level, an inert gas, such as argon, is inserted into the chamber 21, and then an electric discharge occurs due to a negative voltage applied to the electrode 13. As a result of the electric discharge, plasma comprised of ionized gas molecules, neutral molecules, and electrons is generated inside the chamber 21, and the migration speed of the ionized gas molecules is accelerated by the negative voltage so that they finally collide with the target 11. Atoms at the surface of the target 11, having obtained kinetic energy from a collision with the gas molecules, are emitted from the target 11, and the emitted atoms are deposited on the wafer 17 in the form of a thin film. The thickness of the deposited thin film is dependent on the voltage applied to the electrode 13, the level of vacuum in the chamber 21, and the time taken to deposit the thin film.
In the magnetron sputtering method, however, it is very difficult to effectively control the movement of charged particles, particularly secondary electrons in a reactor, which is a critical factor affecting the performance of the magnetron sputtering method. In a case where a horizontal magnetic field is concentrated on a specific region, the target 11 is irregularly etched, and thus particles of the target 11 are deposited on the wafer 17 having an irregular thickness. In addition, it is very difficult for the conventional magnetron sputtering apparatus adopting a magnetron cathode to meet the increasing needs of manufacturing highly integrated devices having a lower line width and processing larger-sized wafers.
A moving magnet-type magnetron sputtering method has been considered superior to other magnetron sputtering methods in terms of film uniformity. FIGS. 2 through 4 are photographs showing various types of conventional moving magnet-type magnetron cathodes. In particular, FIG. 2 is a photograph of a freestyle magnetron cathode, FIG. 3 is a photograph of a collimator deposition system-type magnetron cathode, and FIG. 4 is a photograph of a self-ionized plasma-type single moving magnetron cathode.
These conventional magnetron cathode techniques have proven to be ineffective in processes for a low line width (0.14 μm or below) and a high aspect ratio (5:1 or greater) because they cause asymmetrically deposited thin films, deteriorating film uniformity, and ineffective use of target material accompanied by regionally etching of a target. Previously, there have been significant efforts in the field to improve the conventional cathodes and thus enhance the tendency of target particles to travel straight by improving elements other than a cathode, such as a collimator and a long throw sputter.